# 使用窗口函数求出每个分区（dept_no）按salary降序的排序，再取出每个区排名第一的信息。
select dept_no, emp_no, salary maxSalary
from
(select dept_no, d.emp_no, salary, rank()over(partition by dept_no order by salary desc) ranking
from dept_emp d
join salaries s
on d.emp_no = s.emp_no and d.to_date = s.to_date) a
where ranking=1
order by dept_no